WASHINGTON — President Donald Trump began the week by issuing a pair of early-morning tweets that say American tariffs on imported steel and aluminum will only come off if there’s a new NAFTA agreement that’s fair to the United States.

The messages seem to be leverage for his administration’s renegotiation of the North American Free Trade Agreement, which covers trade between the United States, Canada and Mexico.

"We have large trade deficits with Mexico and Canada," Trump began in his tweets, which contain often-repeated claims but added a new connection between trade talks and the steel and aluminum tariffs he announced Thursday.

We have large trade deficits with Mexico and Canada. NAFTA, which is under renegotiation right now, has been a bad deal for U.S.A. Massive relocation of companies & jobs. Tariffs on Steel and Aluminum will only come off if new & fair NAFTA agreement is signed. Also, Canada must..

"NAFTA, which is under renegotiation right now, has been a bad deal for U.S.A. Massive relocation of companies & jobs. Tariffs on Steel and Aluminum will only come off if new & fair NAFTA agreement is signed," Trump said.

His second tweet said Canada must treat American farmers better and Mexico must do much more to stop drugs from entering the U.S.

…treat our farmers much better. Highly restrictive. Mexico must do much more on stopping drugs from pouring into the U.S. They have not done what needs to be done. Millions of people addicted and dying.

Prime Minister Justin Trudeau — who has said repeatedly that Canada is prepared to deal with a wide range of positions from Trump — said last week that "it just makes no sense to highlight that Canada and Canadian steel or aluminum might be a security threat to the United States."

"That’s why this is absolutely unacceptable and it’s a point we’ve made many times, that I’ve made directly with the president. It’s one that we’re going continue to engage with all levels of the U.S. administration on," Trudeau said during an event in Barrie, Ont.

The Trump administration has also come under political pressure at home to exclude Canada, which a military ally of the United States and its largest supplier of imported steel and aluminium.

Adding the costs of tariffs may make them too expensive for American companies to buy, hurting Canada and other U.S. trade partners, or they may add to the cost of U.S. manufactured goods and construction projects if the costs are passed along to the final consumer.